Soy protein is a material which will become more available with the advent of biodiesel fuel manufactured using soy beans. For every pound of biodiesel produced using soy beans, there are several pounds of soy byproduct produced. If other seed oil, such as canola oil, is used to produce biodiesel, then there will also be protein containing byproducts from those processes as well. Most soy protein today is used in animal feed, but with the forecasts for biodiesel fuel, the animal feed market will be unable to absorb all of the protein containing byproducts.
As a result, there is potentially an abundance of low cost material available for filler applications. Very little has been done with protein in rubber composites. Protein rubber composites have been claimed in floor coverings (U.S. Pat. No. 2,056,958), in adhesives, bonding materials, coatings or impregnating agents (U.S. Pat. No. 2,127,298) and a milk derived protein was shown to give a four fold increase in the modulus of a natural rubber latex based product after being treated with an aldehyde (U.S. Pat. No. 2,931,845). The reinforcing effects of various soy proteins has been studied more recently in carboxylated SBR. See for example the following articles by L. Jong: “Characterization of soy protein/styrene-butadiene rubber composites,” Composites Magazine, Part A 36 (2005), pages 675-682; and “Rubber composites reinforced by soy spent flakes”, Polymer International 54, pages 1572-1580 (2005). Jong showed that soy protein isolate such as ADM's (Archer Daniels Midland, Decatur, Ill.) PRO-FAM®781 can be incorporated into a latex of carboxylated hot emulsion SBR. After coagulation and drying, the masterbatch was as effectively reinforced as a similar masterbatch using N-339 carbon black. Soy spent flakes (approximate composition of 12% cellulose, 17% pectin, 14% protein and 53% insoluble polysaccharide) could also effectively reinforce the same type of elastomer system. In neither of the above-reported studies did Jong use a non-functional elastomer or consider the use of a coupling agent.